As a conventional image formation apparatus, for example, an electrophotographic image formation apparatus includes a charging roller for charging the surface of a photoconductor drum serving as an image bearing member and a developer roller for developing an electrostatic latent image, which is formed on the photoconductor drum, by using toner serving as a developer. For example, a high voltage of about a few hundred V to a few KV (a direct-current high voltage) needs to be applied to this charging roller and this developer roller in order to charge the photoconductor drum and perform development. For generation of such a high voltage, a power supply for high-voltage generation using a wire-wound electromagnetic transformer (hereinafter referred to as a high voltage power supply) is employed.
For example, the structure of a high voltage power supply using an electromagnetic transformer is described in PTL 1, and a desired high voltage can be output to a load.
In contrast to the high voltage power supply using such an electromagnetic transformer, a power supply circuit that makes it possible to reduce the size and weight of a high voltage power supply circuit without using an electromagnetic transformer has been proposed (see PTL 2). PTL 2 discloses the structure for outputting a voltage that an LC resonant circuit obtains by amplifying a voltage (24 V) from a low voltage power supply by using a clock signal serving as a control signal to a boosting circuit including a plurality of diodes and capacitors. With this structure, no transformer is used. Thus, a high voltage power supply can be smaller and lighter.
However, the high voltage power supply described in PTL 2 has the following problems. In the high voltage power supply in PTL 2, the value of a high voltage to be output to a load is a preset fixed value and a signal having a fixed frequency is used as a control signal input to an LC resonant circuit for outputting a voltage. For example, a charging roller and a developer roller serving as loads in an image formation apparatus may have a load change due to environmental variation within the apparatus or wear in the used charging roller and developer roller. If the image formation apparatus does not adjust the voltage output to the charging roller and developer roller in accordance with such a load change, a faulty image may be created in which, for example, the degree of darkness changes. For example, if the high voltage power supply circuit in cited document 2 is applied, it is difficult to perform adjustment in accordance with a load change. Thus, an excessive voltage or an insufficient voltage may be applied to the loads.
The present invention has been made in light of the above-described points, and an object of the present invention is to provide a high voltage power supply that can appropriately adjust an output voltage in accordance with a load change.
Citation List
Patent Literature
PTL 1: Japanese Patent Laid-Open No. 4-352181
PTL 2: Japanese Patent Laid-Open No. 2003-189595